it is extremely crucial. the idea is that the valve will both trap the pressure contained downstream from the valve through the OUT port, and will lock the valve preventing flow after that pressure has been released.

step 1 allow air of desired pressure flow through IN port to OUT port.
step 2 allow pressure to build in pilot port from the OUT port.
step 3 allow valvle to close self given that the pressure downstream of OUT port is ~= pressure upstream of IN port and thus pressure behind pilot is also ~= to pressure upstream of IN port.
step 4 fire canon venting pressure downstream of OUT port. pilot port maintains its pressure via check valve.
step 5 reload cannon
step 6 vent pressure behind pilot opening valve.
return to step 1

wituout this valve several problems occur.
1 the canon cannot be reloaded
2 the canon can never completely vent the chamber into the barrel

it is extremely crucial. the idea is that the valve will both trap the pressure contained downstream from the valve through the OUT port, and will lock the valve preventing flow after that pressure has been released.

I don't get it. What do you want to achieve with this valve ?

Can't you just use a 3 way valve ?
I suspect you don't really need this special valve

this is how this is normally done:
Spend some time analysing it. the main part is the 3 way valve - it first allows filling the chamber and then pilots the QEV and blocks off flow to the chamber at the same time